High frequency apparatus



Sqat. 17, 1940. G. USSELMAN HIGH FREQUENCY APPARATUS Filed Nov. 9, 1937 3 Sheets-Sheet 1 INVENTOR 6. 1.. USSELMAN BY v6. 4%

ATTORNEY.

p 9 G.-L. USSELMAN 00 HIGH FREQUENCY APPARATUS Filed Nov. 9, 19:57 3 Shegts-Shet 2 -u- I I: m 192 1 INVENTOR. 6. L. USSELMAN ATTORNEY.

Sept. 17, 1940.

G. L. USSELMAN 2,215,200

HIGH FREQUENCY APPARATUS Filed Nov. 9, 1937 3 sheetse-fihegti ,1 RECTIFIER 522 l U- u INVENTOR. v L. USSELMAN 208 208' BY JIJM ATTORNEY.

Patented Sept. 17, 1940 UNITED STATES HIGH FREQUENCY APPARATUS George L. Usselman, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 9, 1937, Serial No. 1'7 3,592

4 Claims.

My present invention relates to high frequency apparatus, particularly transmitters for delivery of short waves at high power to a radio antenna.

Heretofore, radio transmitters have been en- 5 closed within a perforated metallic cage. The perforations permitted some degree of cooling and provided a certain degree of electrical shielding. However, the perforations in the shield permitted dust to accumulate upon the parts of the transmitter, frequently giving rise to arc-overs and other undesired actions. There was, therefore, required certain periodic cleanings, increasing the maintenance cost of the transmitter.

To overcome these disadvantages is one object of my invention. In carrying out this object, substantial solid shielding is employed which is substantially airtight, thereby precluding any substantial dust formations on the parts of the apparatus. The solid shielding, obviously, has

the advantage that it provides practically perfect electrical shielding. For ventilation purposes, I

provide, as will be explained more fully hereinafter, a system of forced ventilation which, through the employment of air filters, does not permit of the passage of dust, insects or other undesirable material into the transmitter apparatus.

More specifically, in carrying my invention into air upon the parts of the transmitter which it is particularly desired to be kept cool, such as the filament seals, grid stems and the glass envelopes of the high powered tubes. The air within the transmitter being at a higher pressure than the surrounding air is then forced out through certain natural and other openings provided in the transmitter through control openings provided for the transmitter controlling elements and through other openings especially provided for ventilation.

A feature of the invention resides in making use of the antenna transmission line shields as part of the air circulating system of the transmitter. As constructed in accordance with my invention, these shields serve as chimneys for the air within the transmitter.

In the drawings:

Fig. 1 illustrates a side elevational view of my improved transmitter;

Fig. 1a shows how the vacuum tubes are mounted, and in detail the piping and.- metal bellows effect, air from the building or room in which the connections for-bringing cooling fluid to the tube, jackets;

Fig. 2 is a perspective view of the arrangement of the transmission lines and associated venting elements employed in my transmitter;

Fig. 3 is a plan view showing, diagrammatically, the cooling system and associated push-pull vacuum tube apparatus;

Fig. 4 is an electrical wiring diagram of the transmitter of Fig. 1; and 10 Fig. 5 illustrates a side View of the structural elements constituting certain condensers and associated elements of Fig. (l.

Referring to Figure 1, which is, generally, a I side elevational view of my improved transmitter 15 with the side shielding removed, the various controls 2 are brought out through the front wall 4 of the transmitter. Within the section (5 are mounted the lower power push-pull radio frequency stages such as described in my copending 20 application Serial No. 96,046, filed August 14, 1936. These stages are ventilated with the rest of the apparatus about to be described, but are not provided with specific cooling for any specific apparatus. The entire transmitter apparatus is 25 enclosed within solid sheets of metal and, as before explained, the side nearest the reader has been removed in order to discuss the apparatus within. The top 6 of the transmitter consists'of a pair of perforated metallic plates between which 30' is mounted a layer of felt or cloth. Only one sheet of perforated metal may be employed, in which event the cloth or felt may be suitably mounted beneath the same. Air is drawn in, as indicated by the arrows 8, to the blower Ml operated by motor l2. The air so drawn in is then forced through the pipes M, iii, I8 and 20. Glass tubes 22, 24, 26, 2B are supplied with air from the pipe l6 through rubber connections 36. The glass tubes 22 and 24, as indicated, blow air against the filament seals of vacuum tube 32 and the glass tubes 26, 28 apply air against the filament seals for vacuum tube 34.

Vacuum tubes 32, 34, as will be explained more fully later, are connected in parallel and form one side of a push-pull system. The tubes immediately behind vacuum tubes 32 and 34 are provided with glass pipes 22 to 28 inclusive con nected to the air tube [6 for similar cooling purposes. After cooling the filament seals, the air is forced out into the space about the vacuum tubes 32, 34, as indicated by arrows 36, 35.

The air forced down pipe It and into'pipes l8 and. 20 passes upwardly through two insulating fibre tubes 40, 42. Some of the air in tubes 40, 42 is forced into the glass pipes 44, 46 to points 48, 50 within the tubes 32, 34 cooling the grid stems of vacuum tubes 32, 34. The air forced up through the glass pipes 64, 46 passes inside the grid stem and by virtue of openings which may be provided within the :grid' stems of vacuum tubes 32, 34 over said stems. The escaping air flows back partially over the tubes 44, 45 and escapes into the transmitter, as indicated by the arrows 52, 54. This air passing down over the grid stem serves to cool the same as well as the glass seals adjacent thereto. In this way, the grids of the vacuum tubes are kept at lower'ternperatures since the heat generated at the grids is carried to the grid stems through the grid structure. Another portion of the air coming up through pipes 40 and 42 passes over the tubes 44, 46 and directly over the lower glass walls of vacuum tubes 32, 34, this action being indicated by the arrows 58, 58. This keeps the lower portion of the glass envelope of the tubes cool. The glass tubes 44, 46 are supported in any suitable way, such as by clips, tothe fibre tubes 40, 42.

The glass tubes 44, 46 extend, as illustrated, down into the fibre pipes 40, 42 and well within the hollow grid stems of the vacuum tubes 32, 34. The air, as it leaves the various tubes and pipes, fiows into the space enclosed by the shielding, generally ventilating the remainder of the apparatus therein contained. This air being under pressure, is forced up through the slots 60, 64 and through the holes 66 around insulators 68 up into the twin shields 70, 12 for the transmission lines I4, I6.

As shown in Figure 2, the transmission lines I4,-

uum tubes forms the other side of the push-pull system, in front of which is connected a condenser I00 having V-shaped stationary plates and butterfly shaped or figure 8 shaped rotary plates, as described more fully in my copending application hereinabove referred to. The vacuum tube 32 is strapped by means of strap I02, I84 to metal blocks I08, I08 (note Fig. la). Similarly, tube 34 is strapped to the blocks I08, I08 by means of straps III], II2. As indicated, the anodes of vacuum tubes 32 and 34, blocks I09, I08 and holding straps I04, I02, H0 and H2 are connected directly to one set of stator plates of the condenser I90. In addition, neutralizing condenser II Ii'is also supported by an electrically connected tube to blocks I06, I08. A similar tube, block, strap and neutralizing condenser arrangement is provided immediately behind the system shown and connected to the other set of stator plates of the condenser I00. The entire arrangement is supported by the insulating pedestals I20, I22.

A schematic plan view of the push-pull system is shown in Figure 3, the primed numbers indi-' cating the corresponding elements which cannot be seen in Figure 1 since they are located immediately behind the elements of Fig. 1. It should be borne in mind that this statement applies equally well to the air piping system I 6, I8, 40

and 42, pipes I6, I8 and I4 being duplicated immediately in the rear of Figure 1 and connected to the common header Il The water flow may be traced as follows: Throughthe inlet I88, rubber hose I90, hollow metal conductor I92, into a suitable conduit in block I94. Water then fiows through the metal pipe I96 (note Fig. 1a) through the metal connecting bellows I98 to the lower portion of the water jacket for tube 32 out through upper portion of the jacket and into pipe 290 down through the metal bellows 202 into the lower part of the water jacket for tube 34 out through the elbow 204 in the upper part of the Water jacket for tube 34. The water then flows through the metal bellows 206, pipe 208, bellows 2M through another conduit in block I94 and returns through the metal conductor 208 through the rubber hose 2 I2 to the outlet'pipe 2I4.

As shown diagrammatically in Figure 3, the cooling system is repeated for the rear tubes 32, 34.

of the loop formed by the tubular conductors I92, 208 and I92, 208'. 1

The electrical circuit is shown diagrammatically at Figure 4, the loop 400 being made up as shown in Figures 1 and 3 of the conductors I92, 288 and I92, 208' and the short circuiting bar 2I8.

through blocking condensers 404 and 404' and filter 408 to the transmission lines 14, I6. The purpose of the resistance-inductance combination M0 is to prevent push-push parasitics. It is to be noted that the loop 492 is adjustable with respect to loop 400 to control the loading of the tubes of Figure 4 and conductor M2 is provided connecting loops 400, 402 together so that no difference indirect current potential, which might cause arc-over, shall exist.

The filter 408 includes the series coils 4M, 4M within cylindrical metal shields M6 and M6. The inductances M8 and 4I8' of Figure 4 in practice are illustrated at 4! 8 in Figure 1, it

being noted in Figure 1 that these inductances are made up of straight sections of metallic pipe. On the other hand, the coils 420, 420' of Figure 4 are made up, as shown, of coils 420 of Figure l. The grounded condenser plate 422 of Figure 4 is the vertical metallic plate 422 of Figure 1 and is illustrated in greater detail at 422 in Figure 5.

The condenser plates 430, 430 are so indicated in Figure 5, the variability being obtained by means of the additional plates or disc 432, 434 which are grounded, as is also the plate 422. The condenser elements 430, 430 are supported, as shown, by means of insulators 438, 438 and. additional insulators 438, 438'. The condenser plat-es 450, 450' are identical, but immediately behind the corresponding plates in Figure 5 and, hence, will not be described in detail here.

The input coil 500 is given by the loop 500 of Figure 1 and coupling thereto illustrated by coil 502 of Figure 4 is illustrated at 502 in Figure 1. The ground by-pass condenser 520 of Figure 4 is so referred to in Figure 1. The resistor 522 and coil 524 of Figure 4 are similarly labeled in Figure 1. The resistance-condenser combination 800 and 602 of Figure'4 is so referred to in Figure 1. The filament transformers are mounted above the tubes 604, 603, the connections to the filament leads being evident to one skilled in the art.

, As shown in Figure 1, the antenna loop is An adjustable short circuiting bar 2 I 6; shown in Figure 3, serves to adjust the inductance This, in turn, is coupled to a second loop 402 adjustable with respect to loop 400 connectedhinged at its top so that it may be swun g closer The later section, including the coils, eliminates] to or further away from the inductive output loop of the parallel amplifier tubes. As shown in the schematic wiring diagram, both loops are maintained at the same direct current potential so as to prevent the possibility of short circuits, arcovers and the like during the adjustment of the output loop with respect to the tube output loop formed of the metallic tubular Water carrying conductors and the short circuiting strap.

The neutralizing condensers shown in Figure 1 and referred to diagrammatically in the other figures are of the type described in my copending application hereinabove referred to.

It is to be noted in Figure 1 that metallic bellows are used as flexible links for the metallic pipes conveying water to and from the tube water jackets. Heretofore, it has been proposed to use flexible rubber links for this purpose in order to provide flexibility in connecting the water lines to the tube jackets and supply lines. The rubber links deteriorate with use and are also objectionable since they require frequent shutdown to permit repair of leaks. In addition, I have found that when rubber connectors are used, the ends of the pipes leading to the jackets at the high frequencies involved tend to build up a standing potential wave of such value as to arc-over to the frame of the tube supports. Although this may be obviated by connecting a metal strip to the fluid conductors joined by the rubber hose, there is a possibility of loose connection which is completely eliminated, as is also the possibility of arc-over by utilization of the metal bellows, as shown. I have also found that there is a tendency for high frequency transmitters such as illustrated to set up parasitic oscillations when sections of the water cooling system are connected together by rubber pieces of pipe. These parasitics are also removed by means of the metallic bellows system.

I have also found when rubber connectors are used, it is usually necessary to employ metallic clamps to prevent leakage. I have further found that the metal conduit, the rubber hose and the clamp forms a capacity at the high frequencies involved which tends to cause a considerable capacitive current to flow through the rubber hose, causing its rapid deterioration. I have remedied this by connecting a metallic conductor from the clamp to the metal pipe, but, preferably, I employ the metal bellows system here illustrated since it reduces the number of con nections involved and, necessarily, the number of possibilities of loose connection.

I have also found that my metal bellows system is of decided importance in high frequency work since with rubber connectors and metallic clamps, parasitic oscillations at unwanted frequencies are frequently set up.

The deterioration of the rubber connection explained hereinabove, follows from the use of the equipment in high frequency circuits in which the rubber connectors are subjected to high frequency voltages of relatively large value. These voltages cause currents to flow through the rubber, causing it to heat up and rapidly deteriorate.

It is to be noted that the harmonic filter connected in the antenna transmission line makes use of first inductors in the form of straight sections of pipe. These inductors rest directly upon the condenser-plates of condensers forming another part of the harmonic filter. This section of the condenser, including the low inductance pipe, eliminates the higher frequency harmonics.

the lower frequency harmonics. I

A further feature of the harmonic filter resides in its condenser structure. It isto be noted that the condensers have fixed portions or fixed" capacitive part of the condenser and the hori zontal adjustable disc and the horizontal bend in the condenser plate being the adjustable part of the condenser. The adjustability is obtainedthrough variation in the division of the grounded disc with respect to the right angles condenser plate. The handle of the disc, as illustrated, is brought out through the transmitting housing so that it can be adjusted from the outside of the transmitter wihout necessitating entrance into the interior.

A further feature of the harmonic filter construction, as shown in the drawings, resides in the fact that the low inductance element or pipe section of the filter is mounted directly .upon the blocking condensers.

It is to be noted that all coils of the filter are made of heavy self-supporting copper tubing. This construction is desirable since it prevents heating up due to high current flow and also prevents corona losses.

A further feature of the invention resides in the fact that it is divided into sections and being connected together by the shielded coil. In this way, reaction of one section of the filter upon another is substantially prevented.

Figure 1A is a sectional perspective view of the tubes 32, 34 of Figure 1 and shows in greater detail the piping and metal bellows connections for bringing cooling water to and from the tube jackets.

Having thus described my invention, what I claim is:

1. A transmitter comprising a substantially airtight housing, an air filter attached to the top of said housing, means for drawing air through said filter into said housing, means for forcing the air so drawn in against vacuum tubes mounted within the housing, transmission line shields connected to said housing, and means for permitting egress of air from said housing through said transmission line shields.

2. In combination, electron discharge device apparatus, a metallic housing for said apparatus serving both to shield said apparatus and to prevent the formation of dust thereon, a blower within said housing for forcing air under pressure into said housing, a filter for filtering the air drawn into said blower, air channels communicating with said blower and with the filament and grid seals of said electron discharge device apparatus, a shielded transmission line communicating with said housing, said shielded line having a screen for permitting the escape of air from within said housing.

3. In combination, electron discharge device apparatus, a substantially imperforate metallic housing for said apparatus serving both to shield said apparatus and to prevent the formation of dust thereon, means for filtering air and for forcing the resultant filtered air against certain electrode seals of said electron discharge device apparatus, an electrical circuit associated with said electron discharge device apparatus and located Within said housing, and a conduit for enabling the air forced against said electrode seals to thereafter flow over said electrical circuit, and means for supplying cooling liquid to other electrodes of said electron discharge device apparatus.

4. In combination, electron discharge device apparatus, a metallic housing for said apparatus serving both to shield said apparatus and to prevent-the formation of dust thereon, a blower within said housing for forcing air under pressure into said housing, a filter for filtering the air drawn into 'said blower, air channels 'com municating with said blower and with the filament and grid seals of said electron discharge device apparatus, a shielded transmission line communicating with said housing, said shielded line having a screen for permitting the escape of air from within said housing, means for forcing air against certain electrode seals of said electron discharge device apparatus, and means for supplying cooling fluid to other electrodes of said electron discharge device apparatus.

GEORGE L. USSELMAN. 

